The present invention is related generally to stabilized anaerobic adhesive compositions and is more particularly concerned with a novel composition in which a nitrobenzene is used as a stabilizer.
Anaerobic adhesive systems are those which are stable in the presence of oxygen, but which polymerize in the absence of oxygen. Polymerization is initiated by the presence of a peroxy compound. The cured, cross-linked resins serve as sealants and as adhesives.
Typically, resin monomers are terminated with polymerizable acrylate esters such as methacrylate, ethacrylate and chloracrylate esters, (e.g., polyethylene glycol dimethacrylate and urethane-acrylates (e.g., U.S. Pat. No. 3,425,988) derived according to known urethane chemistry). The other ingredients typically present are an initiator, preferably an organic hydroperoxide such as cumene hydroperoxide, tertiary butyl hydroperoxide and the like. There is also normally provided a stabilizer against free radical initiation, such as a quinone or hydroquinone, in an amount sufficient to prevent premature polymerization of the adhesive due to decomposition of the peroxy compound. There are also preferably present one or more accelerators which are preferably nitrogen-containing compounds such as tertiary amines, imides, sulfamides and the like which promote the rate of cure.
Cure is accelerated by the presence of a suitable metal, such as a transition metal, or its ion.
An anaerobic adhesive is applied to one or both of the surfaces to be joined. When the two surfaces are joined and oxygen excluded, cure is initiated. As is well known, surfaces such as glass may require the application of a suitable accelerator such as a transition metal compound, which increases the rate of cure upon the substantial exclusion of oxygen or air.
Anaerobic adhesives have been well documented in the art as for instance, in U.S. Pat. Nos. 2,895,950; 3,041,322; 3,043,820; 3,203,941; 3,218,305; 3,300,547; 3,435,012, 3,547,851, 3,625,875 and 3,046,262, the disclosures of which are incorporated herein by reference.
Anaerobic adhesive systems are typically supplied from a water-like liquid to a light-weight grease in consistency. One end-use application is to apply the adhesive to the threads of a bolt or mating nut which are then assembled. The adhesive fills the spaces between the threads thereby excluding oxygen and enabling cure. In the normal situation, the metals present in the bolt or the nut accelerate cure.
In spite of the high degree of success that such anaerobic adhesive systems have achieved in the marketplace, a continuing effort is going forward to provide better and/or alternative systems and components therefor. One area of particular interest is the selection of stabilizers as these components determine to a large extent the shelf-life of the product.